The goals of this project are: (l) to develop a self-sustaining source of specific pathogen-free (SPF) rhesus monkeys through the repeated serologic testing of all monkeys at appropriate intervals for the presence of simian retroviruses, simian immunodeficiency viruses, B virus, and through intradermal tuberculin testing to keep the colony TP free. Culture techniques will be used as recommended for Type D retrovirus and B virus, following the recommendations of experts associated with this project (Dr. Nicholas Lerche, California Primate Research Center, and Dr. Julia Hilliard of the Southwest Foundation for Biomedical Research). (2) to maintain genetic diversity within the SPF colonies through screening for the distribution of appropriate genetic markers. The MDPH colony will incorporate into its colony males from other SPF colonies who have been selected on the basis of their ability to bring into MDPH markers either absent, or present in low frequency. Breeding harems will be formed with guidance from the consultant (Dr. Dave Smith, University of California, Davis) to maximize the level of genetic diversity in the MDPH colony. (3) to support AIDS research by providing a stable animal model. Rhesus monkeys must be free of retroviruses to be candidates for the SIV model. Monkeys immunosupressed by retroviruses may have a higher chance of shedding B virus, creating a higher risk to handlers, so B virus free animals are also a must.